Medical apparatus, and surgical method

ABSTRACT

A method for automated implantation of an implant or for an automated augmentation process of hard tissue and/or hard tissue replacement material using a sheath element is provided. The implantation apparatus includes a casing, a converter operable to generate mechanical vibrations the converter inside the casing and displaceable in a longitudinal direction relative to the casing, and a sonotrode coupled to an output location of the converter. A shaft portion with a retention structure is rotationally coupled to the casing and is equipped for cooperating with a rotationally asymmetric element of the sheath element to rotationally couple the casing to the sheath element. An axial coupling is equipped for locking the casing to the sheath element. The shaft portion, the axial coupling and the sonotrode are mutually arranged so that the distal end of the sonotrode may be introduced into a longitudinal opening of the sheath element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is in the field of medical technology. In particular, itrelates to medical devices, medical apparatus and medical methods,especially to implants, apparatuses for implantation, and implantationmethods.

2. Description of Related Art

If screws are anchored in live bone tissue, often the problem ofinsufficient bone stability or insufficient stability of the anchoringin the bone arises. Especially, in trabecular bone tissue, any loadacting on the screw is passed over to only few trabeculae, with adverseconsequences both for the load bearing capability of the screw-boneconnection and for its long-time stability. This is especially severe inosteoporotic or osteopenic or otherwise weakened bone tissue.

One solution of this problem is the use of an alternative anchoringmethod that is suitable also for tissue in which screws are not stable.The publications WO 02/069817, WO 2004/017 857, WO 2008/034 277, and WO2009/055 952 concern anchorage of an implant in bone tissue with the aidof mechanical vibration and a thermoplastic material which isliquefiable by the mechanical vibration, i.e. the thermoplastic materialis capable of being liquefied when vibrated and simultaneously kept incontact with a non-vibrating surface. The thermoplastic material, wherein contact with the bone tissue, is liquefied and pressed into pores orcavities of the bone tissue to constitute, when re-solidified, apositive fit connection with the bone tissue.

A special group of embodiments of implants and implant anchoringprocesses is based on the liquefiable material being inserted(pre-assembled or inserted in situ) in a longitudinal bore of a sheathelement. The sheath element comprises at least one hole in the sheathelement wall, through which the liquefied material is pressed from thelongitudinal bore into the structures (pores or cavities or otherstructures) of the bone tissue or other hard tissue or hard tissuereplacement material in which anchoring is desired. This principle ofpressing liquefied material out of a tube or sleeve element with lateralopenings is for example described in U.S. Pat. No. 7,335,205, U.S. Pat.No. 6,921,264, WO 2009/055 952, WO 2009/010247, WO 2009/010234, and PCTapplication No. PCT/CH 2009/000138, all of which are incorporated hereinby reference.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus, amedical device and a method overcoming drawbacks of prior artapparatuses, methods and devices.

It is another object of the invention to provide an apparatus forcarrying out an implantation or augmentation process with the aid ofmechanical vibration and a thermoplastic material which is liquefiableby the mechanical vibration.

In accordance with an aspect of the invention, an apparatus forimplanting a medical device in hard tissue and/or hard tissuereplacement material or for carrying out an augmentation process in hardtissue and/or hard tissue replacement material is provided. More inparticular, the apparatus is equipped for co-operating with a medicaldevice (implant or augmentation device) that comprises a device bodywith a longitudinal opening (longitudinal bore) extending from aproximal end to a distal direction and one or more holes from thelongitudinal bore outward, so that mechanical vibrations coupled intoliquefiable (especially thermoplastic) material in the longitudinal boreand the simultaneous application of a pressing force into the distaldirection causes portions of the liquefiable material to be liquefiedand pressed out of the longitudinal opening through the at least onehole. In this text, such the body of the medical device having thelongitudinal hole is also referred to as “sheath element”. If the sheathelement is in an opening in hard tissue and/or hard tissue replacementmaterial when liquefiable material is liquefied and pressed out of thelongitudinal opening through the at least one hole, then the materialpressed out of the hole(s) is pressed into structures of the hardtissue/hard tissue replacement material and after re-solidificationanchors the sheath element in the hard tissue/hard tissue replacementmaterial and/or augments the hard tissue/hard tissue replacementmaterial.

The apparatus comprises a casing, and, inside the casing, a converterfor generating mechanical vibrations when appropriately energized. Asonotrode is coupled to the converter. The converter is slidinglymounted within the casing to be displaceable along a longitudinaldirection within the casing. The apparatus further may comprise a springmechanism that, when tensioned, is capable of moving the sonotrode to adistal direction, to excerpt the pressing force of the sonotrode on anelement comprising the liquefiable material of the medical device, andto thereby ensure the necessary propulsion of the sonotrode during theprocess.

The use of a spring mechanism for this purpose has the advantage thatthe pressing force is pre-defined. The spring mechanism may bepre-tensioned manually, and in the tensioned position, the position maybe fixed by an appropriate means, such as a distance holder between alamping lever grip and the casing, or by a bayonet fitting likemechanism.

The apparatus further comprises a retention structure that isrotationally coupled to the casing, i.e. not rotatable relative to thecasing around the implantation axis. The retention element cooperateswith an according not rotationally symmetric element of the medicaldevice to rotationally couple the casing to the sheath element.Furthermore, the apparatus comprises an axial coupling to a sheathelement. At least one of the retention structure, of the axial coupling,and of the interplay between the retention structure and the axialcoupling preferably also angularly couples the sheath element to thecasing, i.e. ensures an angularly stable connection.

The retention structure may be formed by a shaft portion within whichthe sonotrode is guided. For serving as a retention structure, the shaftportion may have a distal end section that has structures that are notrotationally symmetric around the axis and that cooperate withaccordingly fitting structures of the sheath element. For example, thesheath element may have, towards its proximal end, a not rotationallysymmetric outer structure such as a flattening so that the surface hastwo parallel planes, a hexagonal cross section etc. The shaft portionmay have a corresponding inner surface, such as of shaft projectionsengaging the parallel planes, an inner hexagonal structure etc. Theshaft portion may then be shifted, by an axial movement, onto the sheathelement, whereafter the axial coupling is used to fix the sheath elementto the shaft portion. By the effect of such a sheath element outersurface and a shaft portion inner surface, the relative angular positionis also stabilized at least with respect to deflections in one plane.

In accordance with an option, the axial coupling may be a couplingthread. To this end, the shaft portion may encase a directing tube witha thread at its distal end. The directing tube may be rotatable relativeto the casing by manual or automated rotation. The directing tube may bearranged inside the shaft portion and surround the sonotrode.Alternatively, the guiding tube may surround the shaft portion (in whichcase the directing tube may comprise an inner thread engaging with anouter thread of the sheath element, whereas the retention structureengages the proximal end of the sheath element's head portion from aninside). For manual rotation, a turning grip may be present that isrotationally coupled to the directing tube. The retention structure thenprevents rotation of the sheath element when the latter is screwed ontoor into the thread of the directing tube.

In accordance with an alternative option, the axial coupling may be abayonet like coupling. Also in accordance with such an alternativeoption, the shaft portion may encase a directing tube rotatable relativeto the shaft portion, optionally with a turning grip. The directing tubemay cooperate with a fastening mechanism of the sheath element toaxially couple the latter to the apparatus upon a twist movement of thedirecting tube.

In accordance with yet other alternative options, the retentionstructure may comprise a radially movable element that is brought intocontact with the sheath element after the sheath element and theapparatus are brought into the correct relative position. In thesealternative options, the retention structure may comprise the axialcoupling so that no separate element ranging from a position where it isaccessible for the surgeon to the sheath element is required. Forexample, the retention structure may comprise an inwardly protrudingelement that engages into an indentation—such as a groove—of the sheathelement after the radially movable element has been brought into contactwith the sheath element. For example, the retention structure maycomprise two or more jaws with a non-circular inner surface of which atleast one is swivelling. The jaws may each comprise an inner projectingridge to form the axial coupling by engaging behind a correspondingindentation of the sheath element—or vice versa. For locking, thepivoting of the jaws relative to one another may be caused by a lever orby an axially movable clamping ring or any other suitable mechanism.

The retention structure and the axial coupling together fix the sheathelement to the casing of the apparatus. Such a coupling has proven to beadvantageous in many conditions. Together with the spring mechanism orother mechanism ensuring controlled propulsion of the sonotrode duringthe process, it ensures completely reproducible process conditions.

The retention structure ensures that the sheath element is rotationallycoupled to the casing. This brings about a seeming complication, becausea coupling between the casing and the sheath element may not be providedby a simple thread—due to the retention structure, it is not possible tojust screw the sheath element onto the apparatus. However, it has beenfound by the inventors that it is often advantageous to firstly implantthe sheath element in the tissue, for example by placing it like aconventional bone screw. Thereafter, the orientation is to be kept fix,because too much movement of the sheath element relative to the tissueeases the anchoring and/or unnecessarily damages the tissue. Theretention structure makes possible that after placing the sheathelement, the apparatus is brought into position, and firmly coupled tothe sheath element so that in a subsequent process that comprisescoupling energy into a liquefiable element in the longitudinal bore ofthe sheath element the orientation of the sheath element is controlledby the surgeon.

In a group of embodiments, the spring mechanism comprises a first,helical spring that is arranged around a circumferential surface of theconverter and a second spring. The converter is guided within the casingby a first and a second slide bearing. The second slide bearing ismounted slidingly with respect to both, the converter and the casing.The first, helical spring excerpts the spring force between theconverter—or an element fixedly mounted thereto, for example the firstslide bearing—and the second slide bearing. The second spring excerptsthe spring force between the second slide bearing and the casing or anelement fixedly mounted thereto, such as a cap.

The first slide bearing may be a converter ring surrounding theconverter at a distal position and for preferably fixedly mountedthereto. The second slide bearing may be a sliding ring surrounding theconverter at a more proximal position, which position is dependent onthe deflection of the first spring. The first spring may be arranged toexcerpt the first spring force between the first slide bearing and thesecond slide bearing. The second spring may be arranged to excerpt thesecond spring force between the second slide bearing and a cap fixedlymounted to the casing. The first spring may be a helical springencompassing a converter body of the converter.

Generally, in an apparatus with a converter slidingly mounted within acasing, the converter needs to be guided along a substantial portion ofits length (i.e. of its proximodistal extension), or needs to be guidedat two distinct axial positions in order not be subject to undesiredpivoting movements (yaw or pitch movements). If the spring is onlyarranged between the most distal portion of the guiding and the distalend of the casing, as for example taught in WO 2009/010234, then inorder to have a spring having an appropriate spring constant and beingin its linear regime over the entire range of its deflection, the casingneeds to have a length that is substantially greater than the length ofthe converter to provide sufficient space and travel for the spring thatis arranged distally of the converter.

The approach according to the group of embodiments of the invention, incontrast, features the advantage that for a given pre-setdeflection—which may correspond to the length of a liquefiable elementthat is a polymer pin to be liquefied in a sheath element—a total springextension may be essentially the axial extension of a converter bodyplus of the space distally of the converter. Put simply, a springmechanism (comprising the first and second spring in series) of a muchlonger axial extension can be used for a given casing extension. Thisbrings about additional degrees of freedom in choosing the appropriatesprings and thus engineering the travel and pressing force, which areoften important parameters in the implantation or augmentation process.

In another group of embodiments, the converter is guided in the casingby an axially extended bushing that is, for example, fixed to theconverter. The spring mechanism may then engage with the proximal end ofthe bushing, or alternatively, with the proximal end of the converter.

In even further embodiments, the movement of the converter relative tothe casing is brought about by a mechanism different from a springmechanism, such as for example by an electrical motor.

The apparatus may in addition to the casing with the converter,sonotrode and the hereinbefore described elements also comprise anelectronic module that is connected to the converter by a cable. Theelectronic module produces an electric signal of the frequency desiredfor the mechanical vibrations (for example ultrasonic frequency) andfurther may have a feedback control mechanism that adapts the frequencyto the actual situation, for example depending on the mechanical load.The electronic module is generally external to the casing, and the cabletherefore goes through an opening in the casing. In accordance withembodiments of the invention, the casing comprises a cable storage thatstores a portion of the cable, the length of which is enough tocompensate for the entire travel of the converter from the retractedposition to the most extended position—so that the cable does not needto follow the travel by sliding through the opening in the casing.

In embodiments with a spring, the apparatus may have at least one of thefollowing:

-   -   an operating lever for manually retracting the converter with        the sonotrode against the spring force. Such operating lever may        comprise a hand grip or similar.    -   a holding mechanism that holds the converter with the sonotrode        in the retracted position until the mechanism is released. For        example, the holding mechanism may comprise a tilt lever, a        distal end of which may rest against the casing.

The invention further concerns an assembly of an apparatus of the hereindescribed kind with an implant or augmentation element of the hereindescribed kind, wherein a head portion of the implant or augmentationelement is adapted to the retention and coupling structure of theapparatus.

Also a method of implanting an implant is provided. The method is forexample suitable for implanting a bone screw, especially a pediclescrew, but also another bone screw. It is further suitable forimplanting an implant without an outer thread. For example, it issuitable for implanting an implant of the kind described in U.S. patentapplication 61/394,580 incorporated herein by reference in its entirety.

The method comprises the steps of:

-   -   providing the implant with an implant shaft portion and an        implant head portion, the implant head portion being        rotationally asymmetric, the implant shaft portion having a        longitudinal bore and at least one opening ranging from the        longitudinal bore to an outside;    -   driving the shaft portion into bone tissue so that the head        portion protrudes from the bone tissue;    -   after driving the shaft portion into bone tissue, coupling an        apparatus of the kind described hereinbefore to the head        portion, with thermoplastic material being in the longitudinal        opening and with the orientation of the implant head portion        being fixed relative to the casing of the apparatus by the        retention structure;    -   energizing the converter to cause the sonotrode to couple        mechanical vibrations into the thermoplastic material while        causing the sonotrode to be pressed towards the distal direction        and thereby causing portions of the thermoplastic material to be        liquefied and pressed out of the at least one hole into        structures of the bone tissue, and    -   causing the converter to stop and removing the apparatus.

Embodiments of devices and methods in accordance with the invention maybe devices/methods for human surgery, or alternatively for (non-human)animal surgery, especially for surgery of dogs, cats or other pets.

Mechanical vibration or oscillation suitable for devices and methodsaccording to embodiments of the invention that include liquefaction of apolymer by friction heat created through the mechanical vibration haspreferably a frequency between 2 and 200 kHz (even more preferablybetween 10 and 100 kHz, or between 20 and 40 kHz) and a vibration energyof 0.2 to 20 W per square millimeter of active surface. The vibratingelement (sonotrode) is e.g. designed such that its contact faceoscillates predominantly in the direction of the element axis(longitudinal vibration) and with an amplitude of between 1 and 100 μm,preferably around 10 to 30 μm. Rotational or radial oscillation ispossible also.

For specific embodiments of apparatuses, it is possible also to use,instead of mechanical vibration, a rotational movement for creating thenamed friction heat needed for the liquefaction of the anchoringmaterial. Such rotational movement has preferably a speed in the rangeof 10,000 to 100,000 rpm. A further way for producing the thermal energyfor the desired liquefaction comprises coupling electromagneticradiation into one of the device parts to be implanted and designing oneof the device parts to be capable of absorbing the electromagneticradiation, wherein such absorption preferably takes place within theanchoring material to be liquefied or in the immediate vicinity thereof.Preferably electromagnetic radiation in the visible or infraredfrequency range is used, wherein the preferred radiation source is acorresponding laser. Electric heating of one of the device parts mayalso be possible.

In this text the expression “thermoplastic material being liquefiablee.g. by mechanical vibration” or in short “liquefiable thermoplasticmaterial” or “liquefiable material” is used for describing a materialcomprising at least one thermoplastic component, which material becomesliquid or flowable when heated, in particular when heated throughfriction i.e. when arranged at one of a pair of surfaces (contact faces)being in contact with each other and vibrationally or rotationally movedrelative to each other, wherein the frequency of the vibration isbetween 2 kHz and 200 kHz, preferably 20 to 40 kHz and the amplitudebetween 1 μm and 100 μm, preferably around 10 to 30 μm. Such vibrationsare e.g. produced by ultrasonic devices as e.g. known for dentalapplications. For being able to constitute a load-bearing connection tothe tissue, the material at the time of insertion has an elasticitycoefficient of more than 0.5 GPa, preferably more than 1 GPa. Theelasticity coefficient of at least 0.5 GPa also ensures that theliquefiable material is capable of transmitting the ultrasonicoscillation with such little damping that inner liquefaction and thusdestabilization of the liquefiable element does not occur, i.e.liquefaction occurs only where the liquefiable material is at theliquefaction interface to the stop face. The plastification temperatureis preferably of up to 200° C., between 200° C. and 300° C. or even morethan 300° C. Depending on the application, the liquefiable thermoplasticmaterial may or may not be resorbable.

Suitable resorbable polymers are e.g. based on lactic acid and/orglycolic acid (PLA, PLLA, PGA, PLGA etc.) or polyhydroxyalkanoates(PHA), polycaprolactones (PCL), polysaccharides, polydioxanones (PD),polyanhydrides, polypeptides or corresponding copolymers or blendedpolymers or composite materials containing the mentioned polymers ascomponents are suitable as resorbable liquefiable materials.Thermoplastics such as for example polyolefins, polyacrylates,polymetacrylates, polycarbonates, polyamides, polyesters, polyurethanes,polysulphones, polyaryl ketones, polyimides, polyphenyl sulphides orliquid crystal polymers (LCPS), polyacetals, halogenated polymers, inparticular halogenated polyoelefins, polyphenylene sulphides,polysulphones, polyethers, polypropylene (PP), or correspondingcopolymers or blended polymers or composite materials containing thementioned polymers as components are suitable as non-resorbablepolymers. Examples of suited thermoplastic material include any one ofthe polylactide products LR708 (amorphous Poly-L-DL lactide 70/30), L209or L210S by Böhringer Ingelheim.

Specific embodiments of degradable materials are Polylactides like LR706PLDLLA 70/30, R208 PLDLA 50/50, L210S, and PLLA 100% L, all ofBöhringer. A list of suitable degradable polymer materials can also befound in: Erich Wintermantel und Suk-Woo Haa, “Medizinaltechnik mitbiokompatiblen Materialien und Verfahren”, 3. Auflage, Springer, Berlin2002 (in the following referred to as “Wintermantel”), page 200; forinformation on PGA and PLA see pages 202 ff., on PCL see page 207, onPHB/PHV copolymers page 206; on polydioxanone PDS page 209. Discussionof a further bioresorbable material can for example be found in C ABailey et al., J Hand Surg [Br] 2006 Apr;31(2):208-12.

Specific embodiments of non-degradable materials are: Polyetherketone(PEEK Optima, Grades 450 and 150, Invibio Ltd), Polyetherimide,Polyamide 12, Polyamide 11, Polyamide 6, Polyamide 66, Polycarbonate,Polymethylmethacrylate, Polyoxymethylene, or polycarbonateurethane (inparticular Bionate® by DSM, especially Bionate 75D and Bionate 65D;according information is available on datasheets publicly accessible forexample via www.matweb.com by Automation Creations, Inc.). An overviewtable of polymers and applications is listed in Wintermantel, page 150;specific examples can be found in Wintermantel page 161 ff. (PE,Hostalen Gur 812, Hochst AG), pages 164 ff. (PET) 169ff. (PA, namely PA6 and PA 66), 171 ff. (PTFE), 173 ff. (PMMA), 180 (PUR, see table), 186ff. (PEEK), 189 ff. (PSU), 191 ff. (POM-Polyacetal, tradenames Delrin,Tenac, has also been used in endoprostheses by Protec).

The liquefiable material having thermoplastic properties may containforeign phases or compounds serving further functions. In particular,the thermoplastic material may be strengthened by admixed fillers, forexample particulate fillers that may have a therapeutic or other desiredeffect. The thermoplastic material may also contain components whichexpand or dissolve (create pores) in situ (e.g. polyesters,polysaccharides, hydrogels, sodium phosphates) or compounds to bereleased in situ and having a therapeutic effect, e.g. promotion ofhealing and regeneration (e.g. growth factors, antibiotics, inflammationinhibitors or buffers such as sodium phosphate or calcium carbonateagainst adverse effects of acidic decomposition). If the thermoplasticmaterial is resorbable, release of such compounds is delayed.

If the liquefiable material is to be liquefied not with the aid ofvibrational energy but with the aid of electromagnetic radiation, it maylocally contain compounds (particlulate or molecular) which are capableof absorbing such radiation of a specific frequency range (in particularof the visible or infrared frequency range), e.g. calcium phosphates,calcium carbonates, sodium phosphates, titanium oxide, mica, saturatedfatty acids, polysaccharides, glucose or mixtures thereof.

Fillers used may include degradable, osseostimulative fillers to be usedin degradable polymers, including: β-Tricalciumphosphate (TCP),Hydroxyapatite (HA, <90% crystallinity; or mixtures of TCP, HA, DHCP,Bioglasses (see Wintermantel). Osseo-integration stimulating fillersthat are only partially or hardly degradable, for non degradablepolymers include: Bioglasses, Hydroxyapatite (>90% cristallinity),HAPEX® , see SM Rea et al., J Mater Sci Mater Med. 2004Sept;15(9):997-1005; for hydroxyapatite see also L. Fang et al.,Biomaterials 2006 July; 27(20):3701-7, M. Huang et al., J Mater SciMater Med 2003 July;14(7):655-60, and W. Bonfield and E. Tanner,Materials World 1997 January; 5 no. 1:18-20. Embodiments of bioactivefillers and their discussion can for example be found in X. Huang and X.Miao, J Biomater App. 2007 April; 21(4):351-74), JA Juhasz et al.Biomaterials, 2004 March; 25(6):949-55. Particulate filler typesinclude: coarse type: 5-20 μm (contents, preferentially 10-25% byvolume), sub-micron (nanofillers as from precipitation, preferentiallyplate like aspect ratio >10, 10-50 nm, contents 0.5 to 5% by volume).

A specific example of a material with which experiments were performedwas PLDLA 70/30 comprising 30% (weight percent) biphase Ca phosphatethat showed a particularly advantageous liquefaction behaviour.

The material of the sheath element (which may be a screw) may be anymaterial that does not melt at the melting temperatures of theliquefiable material. Especially, the sheath element may be of a metal,for example a titanium alloy. A preferred material is titanium grade5.This material, in addition to being generally suited for implantabledevices, has a comparably low heat conduction. Because of this bad heatconduction, the melting zone arising in liquefiable material and at theinterface to the directing structure is heated quickly, without thesurroundings being heated to too high temperatures. Alternativematerials for the sheath element are other metals like other titaniumalloys, stainless steel, ceramics like Zirconium oxides or Aluminumoxides, or hard plastics such as PEEK etc.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, ways to carry out the invention and embodiments aredescribed referring to drawings. The drawings mostly are schematical. Inthe drawings, same reference numerals refer to same or analogouoselements. The drawings show:

FIGS. 1-3 a pedicle screw being an embodiment of a medical deviceimplantable by an apparatus according to an aspect of the invention;

FIG. 4 a liquefiable element for the pedicle screw of FIGS. 1-3;

FIGS. 5 and 6 an insert element for the pedicle screw of FIGS. 1-3;

FIGS. 7-10 a first embodiment of an apparatus for automated implantationor augmentation;

FIGS. 11-15 a second embodiment of an apparatus for automatedimplantation or augmentation; and

FIGS. 16-18 alternative retention structures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device 41 schematically depicted in FIGS. 1-6 is a surgical implantfor being anchored in hard tissue and/or hard tissue replacementmaterial. More in particular, it is a pedicle screw.

In alternative embodiments, the device may have another function similarto the function of a surgical screw, and/or of an anchor (such as asuture anchor or an implant to which a dental crown is to be mounted),or it may have a “standalone” function, for example by containing asubstance to be delivered to a surrounding tissue, and/or by containinga different device such as an electronic device, etc. Like in all otherembodiments of the invention, the device, if being designed to remain inthe patient's body after surgical operation, may have any function asurgical device anchored in hard tissue and/or hard tissue replacementmaterial may have in surgery. As an alternative to being designed toremain the patient's body after the surgical operation, the devicesaccording to the different embodiments—unless explicitly statedotherwise—may also be a temporary anchor or may be an augmentationdevice, for example as taught hereinafter.

The device 41 is insertable into an opening or a gap or the like of hardtissue and/or hard tissue replacement material, essentially by amovement along an implantation axis 3 that is also considered to be alongitudinal axis of the device. The device comprises a wall portion11.1 that surrounds a longitudinal bore 13 open to the proximal side. Aplurality of holes 14 (four holes equally distributed around thecircumference in the depicted embodiment) range from the longitudinalbore radially outward.

The device further comprises a liquefiable element 21, namely a polymerpin 21 that is adapted to the sheath element to be inserted in thelongitudinal bore 13 from the proximal side.

The device, or more in particular, the pedicle screw 41 comprises ascrew head 42, a threaded section 43, and a distal end portion 44. Thepedicle screw further comprises a longitudinal through bore 13 that,towards the distal end, comprises a narrowed portion so that a shoulder11.5 for stopping the insert element (not shown) inserted from theproximal side is formed.

The thread has a constant outer diameter (major diameter), whereas acore diameter (minor diameter) is larger at the proximal side than atthe distal side. More concretely, in the depicted embodiment, in acentral portion of the threaded section the core diameter graduallyreduces, whereas in peripheral portions the core diameter is constant.In other, alternative embodiments, the core diameter is constant, isgradually reduced along the entire length of the threaded section, orthe core diameter has a stepped characteristic as taught in WO 90/02526,or has any other characteristics. Also, the outer diameter of thethreaded section need not be constant. Generally, the approach accordingto the first aspect of the invention may be combined with any suitableouter thread. Compared to prior art pedicle screws with a longitudinalbore, the bore diameter is comparably large to make insertion of theliquefiable element—that may be a polymer pin—possible. In the depictedembodiment, the bore diameter at the more proximal portion of thethreaded section is 3.1 mm and at the distal portion of the threadedsection is 2.9 mm, whereas the major diameter is 6.6 mm and the minordiameter is between 4.4 mm and 5.3 mm. The resulting wall strength hasproven to be sufficient.

The screw head is flattened and comprises an inner thread that can beused for coupling to an apparatus for automated insertion, as describedhereinafter.

The longitudinal bore 13 is a through bore, making the device suitablefor being guided by a wire in minimally invasive surgery. The throughbore is narrowed towards the distal side so that a shoulder 11.5 isbuilt. The shoulder serves as a stop structure for an insert element 18that terminates the longitudinal opening for the liquefiable elementtowards the distal side.

As shown in FIGS. 5 and 6, the insert element comprises an optionaldirecting structure including walls 15 and the ramp portions 12. Theinsert element comprises a distal tapered portion 19 that together withthe shoulder 11.5 co-operates to form a force fit. The optionaldirecting structure comprises a ramp portion 12 sloping away in aconcave manner from a center around the longitudinal axis. At theradially outer side of the ramp portion, the wall portion of the devicehas the holes 14. At angular positions between the holes, the directingstructure further comprises walls 15 having a proximal edge 15.1 andangularly sub-dividing a portion of the longitudinal bore volumecommunicating with the holes 14.

For the anchoring or augmenting process, the liquefiable element 21 isinserted and brought into a position where it abuts against thedirecting structure (or other structure at least partly limiting thelongitudinal bore towards the distal side). While the sheath element isin contact with hard tissue and/or hard tissue replacement material, theliquefiable element is pressed against the directing structure whileenergy impinges from the proximal side. Under the additional effect ofthe pressing force, the liquefied material of the liquefiable element ispressed out through the holes 14 and into structures, like pores,surface unevenness, inhomogeneities etc. of the hard tissue and/or hardtissue replacement material.

In the anchoring and/or augmentation process, a sonotrode is used tocouple the energy into the liquefiable element. To this end, thesonotrode is pressed against a proximal end face of the liquefiableelement while mechanical vibrations are coupled into the sonotrode. Themechanical vibrations are coupled into the liquefiable element 21, andthe vibration energy is at least partly absorbed at the interface to thedirecting structure—or other distal stop structure—causing the polymermaterial of the liquefiable element to at least locally liquefy at thisinterface. Liquefied and re-solidifying material portions pressed intothe surrounding bone tissue and interpenetrating structures of thelatter strengthen the tissue that may be cancellous bone or accordingreplacement material. In addition, if the device is an implant meant toremain in the patient's body and portions of the liquefiable materialremain, after re-solidifying, in the sheath element, the connectionprovides a solid anchoring.

FIGS. 7 and 8 depict an apparatus 51 for automated implantation of amedical device or for automated augmentation. In the figures, a bonescrew 41, namely a pedicle screw as illustrated in FIGS. 1-5 is coupledto the apparatus 51.

FIGS. 9 and 10 show, in longitudinal horizontal and vertical sections,an enlarged detail of a distal end of the apparatus 51, with a bonescrew 41 of the kind illustrated in FIGS. 10-12 coupled thereto.

The apparatus 51 comprises a handle portion 52, a shaft portion 53, andan intermediate operating knob portion 54. In FIG. 8, also anelectricity supply cable 55 is depicted. The electricity supply cablemay connect the handle portion comprising the converter with a (notshown) electronic module that supplies an electrical signal used forenergizing the converter. The electrical signal may have the frequencyand amplitude required for the process.

Proximally of the ultrasonic converter, a free space within the casingforms a cable storage 60. The cable is coiled up in the cable storage ina manner that upon movement of the converter back and forth between theretracted position and the distal position shown in FIGS. 7-10, thelength of the cable portion that is within the casing 56 remainsconstant. This brings about a substantial advantage during delicatesurgical operations, since the surgeon does not need to guide the cableinto the casing during the advancement movement of the converter and thesonotrode.

For example, the cable may be wound up in the cable storage in a helicalmanner as depicted in the figures.

The handle portion has a handle casing 56 and a cap 57 closing thelatter off proximally. The casing comprises a tube portion 56.1 and ataper portion 56.2. A clamping lever 58 reaches through the cap and isused to pre-load the apparatus by retracting the ultrasonic converter 61arranged inside the casing 56. A cable clamp 59 for the electricitysupply cable 55 is arranged next to the cap 57. The sonotrode 62 iscoupled to the converter 61 and is guided within the shaft 65 by adirecting tube 64 that comprises two slide bushes 69 bearing and guidingthe sonotrode 62. The directing tube 64 is rotationally coupled to aturning grip 67 by means of a fitting key 68. The turning grip and thedirecting tube are rotatable relative to the casing 56 and the shaft 65by manual operation. The taper portion 56.2 of the casing has twoprojecting prongs 56.3 overlapping the turning grip 67 and rotationallyfixing the shaft 65 to the casing 56. The directing tube 64 comprises,at its distal end, an outer thread cooperating with the inner thread ofthe screw head. The screw is mountable onto the apparatus by firstlypositioning the screw at the distal end of the shaft, while shaftprojections 65.1 overlap the flattened portions of the screw head (seeFIG. 10) to hold the bone screw 41, and secondly rotationally moving theturning grip 67 to cause the outer thread of the directing tube toengage into the inner thread of the screw head.

This mounting of the screw is effected while the ultrasonic converter 61is in the retracted, pre-loaded position (not shown in FIGS. 7-10) andwhen a liquefiable material pin (also not shown in FIGS. 7-10) is in thelongitudinal bore of the screw, for example by being attached to thedistal end of the sonotrode or by being pre-assembled with the bonescrew.

The anchoring or augmentation process is initiated while a possibleholding mechanism holding the clamping lever in the retractedposition—such as a removable distance holder placed proximally of thecap 57 or a bayonet fitting like mechanism for the clamping lever—isreleased and the converter 61 generates mechanical vibrations of thesonotrode 62. In the retracted position of the clamping lever 58, theconverter 61 and the sonotrode 62, two springs are compressed against aspring force. In the depicted embodiment both springs are helicalsprings, the first spring 71 arranged around the converter 61.

The first spring 71 is arranged between a distal converter ring 73 and aproximal sliding ring 74. The converter ring 73 is fixedly attached tothe converter 61 and slidingly mounted in the casing 56. The slidingring 74 is also mounted to encompass the converter—near a distal endthereof—but is sliding both, relative to the converter 61 and relativeto the casing 56. The second spring 72 is arranged between the slidingring 74 and the cap 57 (or another element fixed relative to thecasing). In the retracted position, the converter ring 73 is deflectedfrom the position shown in the figures by the full displacement of theconverter. The sliding ring 74 is also deflected, by about half of thefull deflection—depending on the ratio of the overall spring constant ofthe first and second spring in series to the spring constant of thefirst spring.

During the implantation or augmentation process, the springs 71, 72 actto impinge the sonotrode with a pre-defined pressing force in the distaldirection.

Another embodiment of the apparatus is shown in FIGS. 11-15. FIGS. 11-15show the apparatus in a configuration with a pedicle screw loaded by athermoplastic element 21 while the ultrasonic converter 61 is in theretracted, pre-loaded position. The embodiment illustrated in FIGS.11-15, is distinct from the one of FIGS. 7-10 in that it has thefollowing features:

-   -   instead of two springs, only a single, helical spring 71 is        present. A single, axially extended bearing bush 59 replaces the        two bearings of the previous embodiment.    -   The clamping lever 58 has a holding mechanism that holds it in        the pre-tensioned state. The retaining mechanism comprises a        tilt lever 58.3 that is coupled to the handgrip 58.1 and        pivoting relative to a lever shaft 58.2 around a pivoting axis        58.4. The lever shaft is coupled to the converter 61. The distal        end of the tilt lever 58.3 may rest against the cap 57 when the        clamping lever 58 is in the retracted position and the tilt        lever 58.3 is tilted away from the position shown in FIG. 15 by        a few degrees so that the tilt lever serves as distance holder        that holds the converter and the sonotrode in the retracted        position. When the surgeon is ready to start the liquefaction        process, she/he pushes the clamping lever 58 slightly back into        the proximal direction and tilts the tilt lever back into the        position of FIG. 15, whereafter the spring 71 may press the        converter 61 with the sonotrode 62 towards the distal direction        and thereby excerpt the pressing force on the thermoplastic        element 21.

In embodiments of the kind described referring to FIGS. 7-15, instead ofa thread, a directing tube or other element rotatable relative to theshaft could also be used for a bayonet coupling. For example thedirecting tube could comprise one or two projections that can be broughtinto engagement with an inner groove of the sheath element, for exampleby a quarter of a turn.

FIGS. 16-18 yet very schematically depict alternative combinations of aretention structure with an axial coupling. In the variant of FIG. 16, afirst jaw 93 of the retention structure is fixedly connected to theshaft 65, as the shaft projections in the previously describedembodiments. A second jaw 94 belongs to a lever 91 that is swivelingabout a swiveling point 92 so that the surgeon may, by operating thelever, move the second jaw radially inward as shown by the arrows in thefigure, and thereby bring the retention structure into engagement withthe not rotationally symmetric portion of the sheath element (such asthe flattened head of the pedicle screw 41 described in the previousembodiments). In contrast to the previous embodiments, the jaws then maycomprise an axial coupling protrusion 95 that engages in an accordingindentation of the sheath element or vice versa. Due to this, there isno need for a separate directing tube (or other means rotatable relativeto the shaft 65) of a thread or bayonet coupling between the apparatusand the sheath element.

Both jaws, like in the previously described embodiments, comprise inner(i.e. facing to the axis) surfaces that are not rotationally symmetric.

FIG. 17 shows a view of two jaws 93, 94 adjacent the flat portions ofthe head of the screw 41.

Instead of by a lever 91 as depicted in FIG. 16, the jaws 93, 94 may bebrought into engagement with the screw head also by other mechanisms,such as by the mechanism shown in FIG. 18. FIG. 18 very schematicallydepicts a section along the line indicated by the arrows in FIG. 17. Thejaws can be deflected against an elastic force, for example, by axiallymoving a deflecting ring 98 in the direction of the arrow. A (not shown)clipping mechanism or similar may hold the deflecting ring in itsposition once it has been moved. The embodiment of FIG. 18 may comprisetwo or more jaws.

The embodiments of the invention hereinbefore have been illustratedreferring to bone screws with fixed head portions. However, theinvention also works for different kinds of implants or augmentationdevices that have a sheath element and are equipped for releasing athermoplastic material, in a liquefied state, into surroundingtissue/tissue replacement material.

For example, an important class of medical implants is bone screws witha multi-axial head. In such bone screws, the head, in a non-mountedstate, is swiveling relative to the screw shaft. The bone screws maycomprise a clamp mechanism that fixes the relative position of head andscrew shaft when the screw is under the mechanical load. For example, ifthe screw is a pedicle screw, the clamp mechanism fixes the relativeorientation of head and shaft once the rod is introduced in the headportion and fixed with the clip provided for this purpose.

In embodiments of the apparatus according to the invention, theretention structure engages with the screw's head portion. A projectingelement of the apparatus at the same time activates the screw's clampmechanism (for example by pulling the screw head portion into a proximaldirection relative to the screw shaft portion against which latter a forexample plane projection is pressed) so that the clamp mechanism fixesthe orientation of the screw shaft portion relative to the retentionstructure.

Various other embodiments are possible. Especially, the skilled personwill know many possible rotationally asymmetric structure of a sheathelement with which a corresponding structure of the apparatus may engageto form the retention structure.

What is claimed is:
 1. A method of implanting an implant, comprising thesteps of: providing the implant with an implant shaft portion and animplant head portion, the implant shaft portion having a longitudinalbore and at least one opening ranging from the longitudinal bore to anoutside; driving the shaft portion into bone tissue so that the headportion protrudes from the bone tissue; coupling an apparatus to theimplant, the apparatus comprising a casing and, mounted inside thecasing to be displaceable in a longitudinal direction relative to thecasing, a converter operable to generate mechanical vibrations, and theapparatus further comprising a sonotrode coupled to an output locationof the converter, wherein the step of coupling comprises rotationallycoupling the casing of the apparatus to the implant, while thermoplasticmaterial is within the longitudinal bore of the implant or extends intothe longitudinal bore of the implant, energizing the converter to causethe sonotrode to couple mechanical vibrations into the thermoplasticmaterial while causing the converter and the sonotrode to be pressedtowards the distal direction relative to the casing and thereby causingportions of the thermoplastic material to be liquefied and pressed outof the at least one hole into structures of the bone tissue, and causingthe converter to stop and removing the apparatus.
 2. The methodaccording to claim 1, wherein the head portion of the implant is chosento be rotationally asymmetric.
 3. The method according to claim 1,wherein the step of coupling is carried out after the step of drivingthe shaft portion into bone tissue.
 4. The method according to claim 1,wherein causing the converter and the sonotrode to be pressed towardsthe distal direction comprises using a spring to press the converter tothe distal direction relative to the casing.
 5. The method according toclaim 1, wherein the apparatus further comprises a rotatable elementrotatable relative to the casing, the step of coupling the apparatus tothe implant comprising rotating the rotatable element until the implantis axially coupled to the casing.
 6. The method according to claim 5,wherein the implant comprises a thread and wherein rotating therotatable element causes the implant to be screwed onto the apparatus.7. The method according to claim 5, wherein the apparatus comprises ashaft portion extending from the casing to the implant, and wherein theshaft portion rotationally couples the implant to the casing while therotatable element is rotated.
 8. The method according to claim 5,wherein rotation of the rotatable element causes an indentation orprojection of the apparatus to cooperate with a projection orindentation of the implant element to form a bayonet coupling.